Identifying the effects of extinction ratio and substrate birefringence on magneto-optic Kerr effect measurements

The authors characterize the developmental, pilot production, and production quality magneto-optic (M-O) optical digital data disks (OD3). Of key importance is the polarization rotation due to the written magnetic domains. The problem with measuring this rotation is that the M-O signal is masked or contaminated by pick-up head birefringence and the substrate birefringence. The apparent polarization signal which is measured at the M-O differential detector is a complex function of the pick-up head birefringence, substrate birefringence, and actual Kerr rotation. The authors have analyzed the case where the M-O tester or optical drive has drifted from its ideal setting and where they still want to determine the separate polarization rotation contribution of the pick-up head, substrate, and M-O layer. It is shown that there is a sequence of calibrations involving glass substrate non-M-O test disks and the M-O disks under test which permit estimation of the various contributions. The test methods required are described. Typical data on M-O pilot production disks are given